This invention relates generally to the dicing of semiconductor wafers, substrates and hard materials. More specifically, the present invention relates to an in-situ system and method to monitor and measure the wear of dicing saw blades used to dice hard material substrates.
Die separation, or dicing, by sawing is the process of cutting a substrate into its individual circuit die with a rotating circular abrasive saw blade. This process has proven to be the most efficient and economical method in use today. It provides versatility in selection of depth and width (kerf) of cut, as well as selection of surface finish, and can be used to saw either partially or completely through a wafer or substrate.
FIG. 1 is an isometric view of a semiconductor wafer 100 during the fabrication of semiconductor devices. A conventional semiconductor wafer 100 may have a plurality of chips, or dies, 100a, 100b, . . . formed on its top surface. In order to separate the chips 100a, 100b, . . . from one another and the wafer 100, a series of orthogonal lines or xe2x80x9cstreetsxe2x80x9d 102, 104 are cut into the wafer 100. This process is also known as dicing the wafer.
Dicing saw blades are made in the form of an annular disc that is either clamped between the flanges of a hub or built on a hub that accurately positions the thin flexible saw blade. The blade is rotated by an integrated spindle-motor to cut into the workpiece.
Wafer dicing technology has progressed rapidly, and dicing is now a mandatory procedure in most front-end semiconductor packaging operations. It is used extensively for separation of die on silicon integrated circuit wafers.
Increasing use of microelectronic technology in microwave and hybrid circuits, memories, computers, defense and medical electronics has created an array of new and difficult problems for the industry. More expensive and exotic materials, such as sapphire, garnet, alumina, ceramic, glass, quartz, ferrite, piezo-electric materials (PZT), alumina (Al2O3) and other hard, brittle substrates, are being used mainly due to the exploding markets in optical communication components and telecommunications. In addition to these relatively new markets, the traditional markets for hard materials, such as, sensors, automotive components, ceramic ball grid array (CGBA), capacitors, and PZT based surface acoustic wave filters and ultrasound transducers are all exhibiting high growth rates in recent years.
Dicing hard materials is a challenge for the dicing industry. In order to maintain high dicing quality, namely, low top and backside chipping, along with reasonable throughput, the use or resinoid blades is desirable. A resinoid blade has a soft resin based matrix acting as a binder of the diamond particles which, in turn, perform the abrasive dicing process.
Relative to nickel binder type blades, predominately used in the dicing process of integrated circuits, resinoid blades have a blade wear rate that is larger than that of nickel binder type blades by at least an order of magnitude. Although blade wear is application dependent, an example may be useful to illustrate this point. For a resinoid blade used in dicing a glass type substrate, the blade wear is about five micron/meter of dicing length. By contrast, for a nickel binder type blade, used in dicing silicon IC wafers the blade wear is about 0.1 micron (or less) per meter of dicing length.
Conventional methods of monitoring dicing saw blade wear are time consuming. As such, where high blade wear exists processing throughput is significantly reduced. In one such conventional contact method, a blade wear station, based on measuring the height of the blade, is incorporated in the dicing area of the machine. To accomplish this method 1) the height station and the blade tip are brought on top of each other (height station below saw blade tip) through motion in the X-Y plane; 2) the blade is gradually lowered along the z-axis into the height station; 3) the blade tip is brought into contact with the height station sensor to determine the amount of wear of the blade; and 4) the height station and blade are separated from one another and dicing continues. This method is illustrated in U.S. Pat. No. 5,718,615 to Boucher et al.
In another conventional non-contact method, Step 3) above is modified such that the side of the blade interrupts the path of a light source projected between two prisms to determine the height of the blade and thereby the position of the end of the blade. This method is illustrated in U.S. Pat. Nos. 5,353,551 and 5,433,649 to Nishida.
The prior art is deficient, however, in that the conventional methods are time consuming since the blade and height monitoring station must be moved in X, Y and Z directions relative to one another to begin the height measuring process and then separated from one another after the blade wear is determined. It is estimated that this process lasts a minimum of 15 seconds, thereby significantly impacting device throughput, particularly in applications where large blade wear is present.
There is a need to monitor blade wear during wafer or substrate dicing for optimizing the dicing process and maintaining a high cut quality so as not to damage the substrate, often containing electronic chips or optoelectronic devices valued in the many thousands of dollars. There is also a need to perform fast monitoring so as to reduce cost of ownership.
In view of the shortcomings of the prior art, it is an object of the present invention to help optimize the monitoring of dicing saw blade wear.
The present invention is a device mounted on a cooling block and a spindle of a dicing saw for monitoring dicing saw blade wear. The device has a transmitter to emit light onto a side surface of the saw blade and a receiver for receiving a portion of the light not blocked by the saw blade.
According to another aspect of the invention, a processor is coupled to the receiver for determining wear of the saw blade based on an output from the receiver.
According to still another aspect of the invention, a photoelectric sensor is used to sense the wear of the saw blade.
According to yet another aspect of the present invention, predicted wear of the blade is determined and communicated to the operator and/or control center.
According to a further aspect of the invention, the wear rate of the saw blade and/or an estimated time for replacement of the saw blade may be communicated to the operator or control center.
These and other aspects of the invention are set forth below with reference to the drawings and the description of exemplary embodiments of the invention.